1. Field of the Invention
Individuals often report an immediate increase in dentin postoperative hypersensitivity or pain to sudden extremes of thermal stimuli to either a particular tooth or a group of teeth. This may occur following either the replacement of a restoration due to a recurrent carious lesion subjacent to a previously placed restoration, the initial placement of an existing amalgam alloy or a tooth colored resin composite restorations or following the bleaching of teeth with power (light, heat or other) assisted forms of tooth whitening systems. Patients may simply be cautioned by the dentist to be aware of an immediate increased feeling of pain to a rapid jet of air, cold drinks, to chewing forces of occlusion or to other factors such as acidic foods. Stimuli, such as cold water, cool air, osmotic gradient shifts, or sweet or acidic solutions at the cavosurface margin of a restoration have all been shown to cause an immediate increase in the dentin pain response. Dentists may simply call this phenomenon as patient dentin pain (postoperative hypersensitivity/DPH) or simply dental discomfort. Often patients are told by the dentist to simply wait a few days or weeks and that the pain of discomfort will become less and less, and eventually that it should go away.
The acute, sharp, piercing pain of dentin pain is often a fairly common complaint among many patients who have recently received an amalgam alloy or resin composite restoration in vital dentin that has been treated with a conventional dentin liner such as a calcium hydroxide Ca(OH)2 material such as Dycal(copyright) or Life(copyright). Dentin postoperative hypersensitivity generally occurs with the normal physiological breakdown of the smear layer or its removal at the cavosurface margin due to oral fluids which reach an acidic pH of 2.7 to more neutral at pH6.0.
If the dentist uses any type of instrumentation, for example, rotary instrumentation with a drill or bur, scraping or polishing with any sort of hand instrument, will leave a layer of debris on the tooth surface called a smear layer. The breakdown of the smear layer by physiological action or by the dentist, opens and exposes the dentinal tubule complex to a bi-directional flow of fluids from the dental pulp (Pashley, 1981 Arch. Oral. Biol. 26: 703-706). It is this increased bidirectional fluid flow which is responsible for the patients"" dentin postoperative hypersensitivity to cold or rapid air flow.
Many patients experience dentin postoperative hypersensitivity when an existing amalgam alloy or a resin composite restoration and its underlying Ca(OH)2 base of Dycal(copyright) or Life(copyright) washes out or is removed and the dentin loses its biological seal or simply feel the pain from discomfort due to premature occlusal contact or thermal or cold extremes.
The physiological mechanism for dentin pain following placement of either an amalgam alloy or a resin composite restoration has been explained as being due to the breakdown or loss of the smear layer which then results in an immediate increased flow of pulpal fluids through its micro channel complex (Pashley, et al. 1984 Arch. Oral. Biol. 29:65-68). This increase in flow may be 94% greater than the normal physiological flow of fluids through the normal dentin substrate.
The present invention relates to the use of an acid resistant film forming liner material that occludes the dentinal tubules to decrease dentinal sensitivity, acid penetration and discomfort.
2. Summary of the Related Art
The aforementioned Pashley et al., articles disclose the hydrodynamic theory of flow and displacement of the contents of dental tubules under various conditions. Pain stimuli is transmitted to nerve structure by hydrodynamic movement of force in the tubules within the dentin. Prior art methods of alleviating pain during dental restoration procedures include preparing a cavity in a tooth to receive restorative material with a cavity liner or cavity varnish. The material allegedly decreases the permeability of the dentin to other materials placed in the cavity during this restoration in addition to blocking the attack of any microleakage, that is, contaminants from the oral fluids that may attempt to penetrate the cavity in the event that the restorative material permits microleakage around its margins with the tooth. Prior art cavity varnishes frequently contain organic gums dissolved in organic solvents. The organic solvent evaporates leaving a film of the organic gum on the dentin.
These cavity lining agents are composed primarily of water and soluble organic materials which is often placed on a liquid layer that covers the surface of the dentin without any bonding. This may weaken any adherence of the cavity varnish to the tooth surface and may cause leaking.
A natural cavity liner is microcrystalline debris which is found in the surface of dentin which is cut and is referred to as a smear layer. The smear layer occludes the orifices of the dentinal tubules to the point where bacteria cannot access the tubules. However, the smear layer is often destroyed due to the acidity in the oral cavity and the presence of microleakage around the filling material which is in contact with a cavity varnish.
The prior art also includes the use of oxalate salts to desensitize hypersensitive dentin or cementum surfaces on teeth, for example, as disclosed in U.S. Pat. No. 4,057,621. U.S. Pat. No. 4,538,990 discloses a two-step method using different oxalate acids salts to decrease the permeability of a dental cavity prepared for receiving a restorative material. The method involves sequential application of the oxalate salts to the smear layer. First, a 1 to 30% weight to volume neutral oxalate salt solution, for example, dipotassium oxide, is applied and then followed within one or two minutes by an application of 0.5 to 3% weight to volume percent of an acidic oxalate solution, such as monopotassium mono hydrogen oxalate. The neutral oxalate forms large calcium oxalate crystals over the dentin surface and the acid oxalate forms smaller crystals around the previously precipitated larger crystals to form a uniform layer of crystals.
U.S. Pat. No. 2,746,905 discloses the use of dehydroacetic acid and the soluble salts to maintain the pH of the mouth to about 5.2 to prevent the dissolution of inorganic tooth enamel material which includes the use of oxalate in the composition as an enamel protective agent to increase the resistance of the tooth to acid attack.
In contrast to the above literature and patents, the present invention utilizes a specific oxalic acid salt, oxalate acid potassium salt, dihydrate, 99% which when applied to the surface of the tooth penetrates into the tubules and fibriles of the dentin layer. The oxalic acid potassium salt dihydrate, or it may be simply referred to as potassium oxalate dihydrate, eliminates fluid movement within the tubules and therefore limits the dentin to be incapable of transmitting painful stimuli to the pulp in the form of fluid movement Therefore, no pain or discomfort is felt by the patient for long periods of time.
The present invention relates to a method of utilizing a solution of oxalic acid potassium salt, dihydrate, 99% as referred to hereinafter as potassium oxalate dihydrate, to react with ionized calcium in the dentinal fluid forming an insoluble white precipitate of calcium oxalate that includes the dentinal tubules. This action leads to decreased permeability of dentin, decreased acid penetration of dentin and decreased dentinal sensitivity. The solution of potassium oxalate dihydrate contains about 1.5 to about 10% by weight oxalic acid potassium salt dihydrate and has a pH ranging from about 2.0 to about 4.0.
It is an object of the present invention to provide a method of using a solution of oxalic acid potassium salt dihydrate to decrease permeability of dentin.
Another object of the present invention is to provide a method of using a solution of oxalic acid potassium salt dihydrate to decrease dentin sensitivity.
Another object of the present invention is to provide a method of using a solution of oxalic acid potassium salt dihydrate to decrease acid penetration of dentin.
And, yet another object of the present invention is to provide a simple diagnostic test to determine if dental pain or discomfort is reversible or irreversible.
Another object of the present invention is to provide a method to solubilize oxalic acid potassium salt dihydrate in water so that it is available in a dosage form to serve as a desensitizing agent.